The invention relates to a process for cleaning solids-laden gas, and to an apparatus for carrying out such a process.
A great variety of processes and devices are known for removing solid contamination from gases such as flue gases and product gases. Especially in industrialized and heavily crowded areas, flue gases must be cleaned thoroughly prior to emission into the atmosphere in order to minimize environmental pollution. One example of cleaning product gases can be found in the purification of crude synthesis gas prior to further processing or use of the gas. Such a purification is required in order to prevent fouling of the equipment used for further processing or application of the gas.
The various types of gas cleaning devices available at present can be divided into two groups, viz. the so-called dry cleaning devices and the so-called wet cleaning devices. Dry cleaning devices, such as filters and cyclones, are suitable for removing relatively coarse solids from gases. If very small solid contaminations, having sizes less than about 5 microns, are to be removed, filters might be effective. However, such filters have the drawback that their size is normally rather large. In order to increase the separation efficiency or to obtain a more compact unit, use can be made of devices of the wet cleaning type. In these latter devices, the solid contaminations of a gas stream are caught and entrained by a washing liquid which is atomized in the gas stream.
An apparatus for wet cleaning of solids-laden gas is known from U.S. Pat. No. 3,142,548. In this patent, a so-called venturi scrubber is disclosed, wherein during operation a solids-laden gas is caused to flow through a venturi-shaped device. Upon passing the throat of said device, the gas stream with the very fine dispersed solids is considerably accelerated, while simultaneously, washing liquid is added to the gas stream at a rather low velocity. The washing liquid is dispersed in a fog-like fashion in the gas. The large relative solids/droplets velocity will result in the formation of agglomerates of solid contaminations and washing liquid droplets due to inertial impaction. These agglomerates are subsequently removed from the gas with the aid of mechanical separation means, formed by a filter mat in the above known cleaning apparatus.
The above known wet-cleaning device has a high separation efficiency for fine solids. However, very fine solids, on the order of magnitude of less than 1 micron, tend to remain in the gas stream when using this known wet-cleaning device, unless very high pressure losses for the gas phase are permitted in the venturi-throat.
The ever-increasing production of flue gases and product gases, nonetheless, requires more advanced separating procedures and equipment of this kind, having very high separation efficiency, even for the very fine particles, but at an acceptable pressure drop for the gas phase. An object of the present invention, therefore, is to provide a process for cleaning solids-laden gases which has a higher separation efficiency than the known separating methods, without, however, reducing the throughput and considerably increasing the gas phase pressure drop.